ASFs will foster mouse and even rat pups. They won't kill young babies. The mothers anyway. It isn't in their nature at all. I've done it before too. Just be sure to pull those babies as soon as they wean if you don't feed them off. The ASFs will raise them up with no problems though.

As long as there are other nursing ASF babies in there, you can always put other rodent babies in safely if they are young enough.